These include allowing staff in London to work a shorter working day because it takes time to get into work and getting extra days off as “privilege days”.

Cabinet Office minister Francis Maude and Sir Bob Kerslake, the head of the civil service, set out last year plans to cut down on staff perks that were out of step with modern working.

Mr Maude had asked departments to identify terms and conditions “that are beyond what a modern employer would provide”, according to sources, prompting reports that they would be axed.

In January Katherine Kerswell, director-general of civil service reform at the Cabinet Office, who is pushing through the changes, said: “Each department, as its own employer, is pursuing its own negotiations around its terms and conditions of service.

“They’re all beginning that now, and it’s going to be a tough conversation but it’s a very positive process”.

However, Mr Maude and Sir Bob have now admitted the changes – which had caused anxiety among unions - will only apply to new recruits or to newly promoted officials.

The change will mean perversely that civil servants who are neither good enough to be promoted, or hired from elsewhere, will be left with the best contractual perks.

Given that Whitehall currently is in the grip of a recruitment freeze, it might mean the changes only affect a very small proportion of officials.

The minister disclosed the change in a letter to the entire 451,000-strong civil service last month, co-written with Sir Bob Kerslake, the head of the civil service.

In the letter, sent last month, they said: “When we talk to civil servants, ‘Terms and Conditions’ are often raised.

“The Civil Service will continue to offer employment terms that are among the best available. The proposed changes will apply to new entrants and, potentially, staff on promotion.”

The Cabinet Office has now written to every Government department urging it to look at reforming six different employment areas for new recruits and ambitious civil servants who are promoted.

These include cutting down on holidays, “occupational sick pay” and stricter probation rules.

The departments should also stop letting civil servants in London work an hour less than others because it takes longer to get to work and remove a “mobility clause” which stops them working away from the office.

It emerged last year that some officials were able to use their contractual terms to work nine-day fortnights by cutting short their lunch breaks and staying in their offices until 6pm.

Civil servants are automatically given an extra two and a half ‘privilege’ days off every year, including on Maundy Thursday and the Queen’s Birthday.

It is likely that some of these will be rolled into a generous allocation of six weeks’ annual leave plus eight bank holidays.

A Cabinet Office source said: “Some terms and conditions are contractual and cannot be changed while civil servants are in post, which is why departments may choose to change them for new entrants or those on promotion.”

Unions warned that the changes would effectively put people off from being promoted. Rob O’Neill, assistant general secretary of the First Division Association, told Civil Service World: “We are arguing that it will be a disincentive to go for promotion.”

Tory MPs criticised the Coalition for failing to change the terms and conditions for all staff – and effectively punishing those who were ambitious or were recruited.

Priti Patel said: “They should apply changes across the board. In these days when everyone is doing more for less, we have got to make sure we change the culture of the civil service, by rewarding it when it is a success and not when it is a failure.”

Charlie Elphicke, a member of the Commons Public Administration select committee which reviews the civil service’s work, added: “In the private sector, terms and conditions can be changed for existing employees with a consultation and under performing workers can be put on performance review and dismissed if they don’t make the grade.

“Why should civil servants be any different? Given the state of the nation’s finance, the approach needs to be more business-like and we need to do more to get on top of the civil service unions.”

The changes are being pushed through by Clare Sumner, a former Downing Street private secretary and Katherine Kerswell, a former chief executive of Kent County Council who quit after 18 months in the post with a £420,000 pay off

Speaking earlier this year, Miss Kerswell admitted that some the terms and conditions in the civil service did not pass what she described as “the pub test”.

She told Civil Service World: “If [civil servants] talk to their friends and say: ‘They’re doing this to me at work,’ and start sharing what terms and conditions their colleagues have in terms of sick pay, in terms of leave, in terms of training opportunities, actually, when you look at what the civil service is offering…

“I think it’s a very positive employment package and it rates very well against a lot of local government.

“It’s difficult when people feel they’re losing something; but when you do the ‘pub test’, I think you can see it’s a balanced package that’s being offered.”

A spokesman for the Cabinet Office said: “Civil Service terms and conditions are being reviewed through the Civil Service Reform Programme.

“The Civil Service will remain a good employer so it can attract and retain high quality staff. However some of its conditions have become outliers in comparison to the wider public and private sector and these will be addressed.”

The Cabinet Office is already to set the example by changing terms and conditions by the end of April. It is hoping that other departments will follow suit and introduce the new contracts over coming months.

A Cabinet Office source added: “Our aim has been to adopt best practices from the private and public sectors, creating an employment package that a good, modern employer would offer and tackling those terms that could leave the Civil Service open to criticism.

“To achieve that aim our proposal is to introduce these new SCS terms for new starters and those on promotion by the end of April this year.”

Sources close to Mr Maude said other feather-bedded perks, such as the little used clothing allowance for staff to replace items they damage on Government property, can be phased out without renegotiating contracts.

Letter from Francis Maude and Sir Bob Kerslake to civil service, March 2013

Dear Colleague,

Eight months ago we published the Civil Service Reform Plan. We set out our vision for an exceptional Civil Service that will deliver the best for Britain by becoming more skilled, less bureaucratic and more unified.

This action plan was based heavily on feedback from you. We listened to what frustrates and motivates civil servants. You have highlighted the need for improved workplaces and IT, fairer performance management, and less bureaucracy. And we are visiting civil servants across the country to continue to hear your views and discuss reform. The success of the Civil Service Reform Plan hinges on you – we want to harness your commitment and ideas. We want to hear about your experiences of delivering the best through the new Civil Service Reform pages on the Civil Service website.

One key frustration is the failure to address under-performance and reward the best. To address this a new Civil Service Competency Framework will be in place across the Civil Service from April. The Framework will improve performance management, and will make it easier for you to identify your learning needs and apply for jobs in different departments.

The digital transformation of government is underway. We are shifting the first wave of transactional services to digital channels and we have expanded GOV.UK as the online home for all government services and information. We will ensure that you have the right skills to do your job in a digital world. You will hear more about this in the coming year.

In the current financial climate the Civil Service must be much more joined up, sharing services, skills and resources. Departments and arms-length bodies will work together to share functions such as HR, procurement, finance and payroll – delivering savings and making the Civil Service more unified.

On Monday, as part of our commitment to improve policymaking, we launched the What Works Network, a series of centres which will provide cutting edge research to all those commissioning and providing public services.

When we talk to civil servants, Terms and Conditions are often raised. The Civil Service will continue to offer employment terms that are among the best available. The proposed changes will apply to new entrants and, potentially, staff on promotion.

We are also aware of the importance you attach to positively promoting the good things the Civil Service does. We will play our part but every civil servant can be an ambassador for what the Civil Service does well. The work you do matters – civil servants quite simply keep this country’s public services going. We should all be proud of our roles, while at the same time focused on working to deliver more effective and efficient services - and challenging colleagues to do the same. If we do all this, while holding fast to our core values of integrity, honesty, objectivity and impartiality we will be an exceptional Civil Service delivering the best for Britain.